Low Energy System and Method of Desalinating Seawater

ABSTRACT

A low energy water treatment system and method is provided. The system has at least one electrodialysis device that produces partially treated water and a brine byproduct, a softener, and at least one electrodeionization device. The partially treated water stream can be softened by the softener to reduce the likelihood of scale formation and to reduce energy consumption in the electrodeionization device, which produces water having target properties. At least a portion of the energy used by the electrodeionization device can be generated by concentration differences between the brine and seawater streams introduced into compartments thereof. The brine stream can also be used to regenerate the softener.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims benefitunder 35 U.S.C. 120 to co-pending U.S. patent application Ser. No.14/539,691, titled LOW ENERGY SYSTEM AND METHOD OF DESALINATING WATER,filed on Nov. 12, 2014, which is a divisional application of and claimsbenefit under 35 U.S.C. 120 to U.S. patent application Ser. No.12/679,310, titled LOW ENERGY SYSTEM AND METHOD OF DESALINATING WATER,filed on Jul. 16, 2010, issued on May 5, 2015 under U.S. Pat. No.9,023,215, which is a national stage application of and claims benefitunder 35 U.S.C. 371 of International Application No. PCT/US2008/010969,filed on Sep. 22, 2008, titled LOW ENERGY SYSTEM AND METHOD OFDESALINATING WATER, which claims benefit to U.S. Provisional PatentApplication No. 60/981,855, titled ENERGY EFFICIENT DESALINATION SYSTEM,filed on Oct. 23, 2007, and to U.S. Provisional Patent Application No.60/974,298, titled ENERGY EFFICIENT DESALINATION SYSTEM AND METHOD,filed on Sep. 21, 2007, each of which is herein incorporated byreference in its entirety for all purposes.

BACKGROUND

1. Field of Invention

This invention relates to systems and methods desalinating seawater and,in particular, to low energy consuming systems and methods ofdesalinating seawater involving staged electrodialysis devices andelectrodeionization devices having concentration-based potentialhalf-cell pairs.

2. Discussion of Related Art

Sea water desalination was dominated by thermal processes such as vaporcompression stills, multiflash distillation and others. Most thermalplants are located where there was abundance of power available fordesalting sea water. Electrodialysis was typically used for desalting ordesalinating brackish water. Reverse osmosis desalination systems arenow more prominent because of such systems have lower power requirementsand have lower capital and operating and maintenance costs, compared tothermal systems. The use of energy recovery devices in reverse osmosissystems has further reduced the energy consumption. However, reverseosmosis technology typically require at least about 2.5 kWh/m³. Thermalprocesses will continue to be high in power consumption due to phasechange needed for desalination. If waste heat is available thenprocesses such as membrane distillation may be used with powerrequirements of as low 1.5 kWh/m³.

SUMMARY

The present use of electrodialysis devices operated at low powerconsuming conditions and electrodialysis device potential generatinghalf-cell pairs provide desalination system that relatively have lowerenergy requirements compared to conventional reverse osmosis-basedseawater desalination systems.

One or more aspects of the invention can be directed to anelectrodeionization device comprising a first depleting compartmentfluidly connected to a source of water having dissolved solids therein,the depleting compartment defined at least partially by a cationicselective membrane and a first anionic selective membrane; a firstconcentrating compartment fluidly connected downstream from a source ofa first aqueous liquid having a first dissolved solids concentration,and in ionic communication with the first depleting compartment throughthe cationic selective membrane; and a second depleting compartmentfluidly connected downstream from a source of a second aqueous liquidhaving a second dissolved solids concentration that is greater than thefirst dissolved solid concentration, and in ionic communication with thefirst concentrating compartment through a second anionic selectivemembrane.

One or more aspects of the invention can be directed to devices fortreating water having dissolved ionic species therein. The device cancomprise, in some embodiments, a first depleting compartment fluidlyconnected to a source of the water, and at least partially defined by afirst anion selective membrane and a first cation selective membrane; afirst concentrating compartment fluidly connected to a source of a firstaqueous solution having a first concentration of dissolved solids, inwhich the first concentrating compartment is typically in ioniccommunication with the first depleting compartment through one of thefirst anion selective membrane and the first cation selective membrane;and a second depleting compartment fluidly connected to a source of asecond aqueous solution having a second concentration of dissolvedsolids that is greater than the first concentration of dissolved solids,in which the second depleting compartment is typically in ioniccommunication with the first concentrating compartment through one of asecond cation selective membrane and a second anion selective membrane.

One or more aspects of the invention can be directed to a seawaterdesalination system. The desalination system can comprise at least onefirst electrodialysis device including at least one first depletioncompartment having a first depletion compartment inlet fluidly connectedto a source of seawater, and a first depletion compartment outlet, andat least one first concentration compartment having a first depletioncompartment inlet and a first depletion compartment outlet; at least onesecond electrodialysis device including at least one second depletioncompartment having a second depletion compartment inlet fluidlyconnected to the source of seawater, and a second depletion compartmentoutlet, and at least one second concentration compartment having asecond concentration compartment inlet fluidly connected to the sourceof seawater, and a brine outlet; at least one ion exchanging unit havingan ion exchanger inlet fluidly connected to at least one of the firstdepletion compartment outlet and the second depletion compartmentoutlet, and an ion exchanger outlet; and at least oneelectrodeionization device having a first depleting compartment fluidlyconnected to the ion exchanger outlet, the depleting compartment definedat least partially by a first cationic selective membrane and a firstanionic selective membrane, a first concentrating compartment fluidlyconnected to the source of seawater, and in ionic communication with thefirst depleting compartment through the first cationic selectivemembrane, and a second depleting compartment fluidly connecteddownstream from the brine outlet, and in ionic communication with thefirst concentrating compartment through a second anionic selectivemembrane.

One or more aspects of the invention can involve a desalination systemcomprising a source of water which can at least partially have or beseawater; a means for selectively reducing a concentration ofmonoselective species in a first seawater stream to produce a firstdiluted stream; a means for increasing a dissolved solids concentrationin a second seawater stream to produce a brine stream; means forexchanging at least a portion of divalent species for monovalent speciesin the first diluted stream, wherein the means for exchanging typicallyhas a second diluted stream outlet;

and an electrochemical separation device. The electrochemical separationdevice typically has a depleting compartment fluidly connected to thesecond diluted stream outlet, and a means for providing aconcentration-induced electrical potential in ionic communication withthe depleting compartment.

One or more further aspects of the invention can be directed to anelectrodeionization device comprising a depleting compartment fluidlyconnected to a source of water having dissolved solids therein, whereinthe depleting compartment defined at least partially by a cationicselective membrane and a first anionic selective membrane, and aconcentration half-cell pair in ionic communication with the depletingcompartment. The concentration half-cell pair typically comprises afirst half-cell compartment fluidly connected to a source of a firstaqueous liquid having a first dissolved solids concentration, and inionic communication with the depleting compartment through one of thecationic selective membrane and the first anionic selective membrane,and a second half-cell compartment fluidly connected downstream from asource of a second aqueous liquid having a second dissolved solidsconcentration that is greater than the first dissolved solidconcentration, and in ionic communication with the first half-cellcompartment through a second anionic selective membrane.

One or more still further aspects of the invention can be directed to amethod of desalinating seawater comprising reducing a concentration ofmonovalent species of seawater in a first desalting stage to producepartially desalted water; producing a brine solution from seawater,wherein the brine solution typically has a total dissolved solidsconcentration that is at least twice the concentration of totaldissolved solids in seawater; introducing the partially desalted waterinto a depleting compartment of an electrically-driven separationdevice; and creating a concentration-induced electrical potential in aconcentration cell pair of the electrically-driven separation devicewhile promoting transport of at least a portion of dissolved speciesfrom the partially desalted water in the depleting compartment into acompartment of the concentration cell pair.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing.

In the drawings:

FIG. 1 is a schematic flow diagram of a system in accordance with one ormore embodiments of the invention;

FIG. 2 is a schematic flow diagram of a system in accordance with one ormore further embodiments of the invention;

FIG. 3 is a schematic flow diagram of a seawater desalination system inaccordance with one or more embodiments of the invention;

FIG. 4 is a schematic representation of a portion of anelectrodeionization device which can be utilized in one or more systemsin accordance with one or more aspects of the invention;

FIG. 5 is a schematic representation of a portion of anelectrodeionization device in accordance with one or more aspects of theinvention;

FIGS. 6A and 6B are schematic representations of portions ofelectrodeless continuous deionization devices in accordance with one ormore aspects of the invention;

FIG. 7 is a graph illustrating the predicted energy requirements inaccordance with one or more aspects of the invention;

FIG. 8 is a schematic representation of a Donnan-enhancedelectrodeionization (EDI) module in accordance with one or more aspectsof the invention;

FIGS. 9A and 9B are schematic representations of a system in accordancewith one or more aspects of the invention;

FIGS. 10A and 10B are schematic representations of electrodialysistrains that can be utilized in accordance with one or more aspects ofthe invention.

FIGS. 11A and 11B are graphs showing the energy required in treatingsynthetic saltwater (“NaCl solution”) and seawater relative to targetproduct total dissolved solids concentration, utilizing electrodialysisdevices with standard ion selective membranes (FIG. 11A) andmonoselective membranes (FIG. 11B) in accordance with one or moreaspects of the invention; and

FIGS. 12A and 12B are graphs showing the fractions of cations (FIG. 12A)and anions (FIG. 12B) during treatment of seawater relative toelectrodialysis stages utilizing monoselective membranes, in accordancewith one or more aspects of the invention.

DETAILED DESCRIPTION

The present invention is directed to a treatment system, which in someaspects, embodiments, or configurations, can be a water treatmentsystem. Some particularly advantageous aspects of the invention can bedirected to seawater treatment systems or desalination systems andtechniques involving seawater treatment or desalination. The systems andtechniques of the invention can advantageously provide treated water byutilizing differences in concentrations to create potential or motiveconditions that facilitate transport of one or more migratable dissolvedsolids in the water to be treated. Further aspects of the invention canbe directed to systems and techniques that provide potable water fromseawater or brackish water.

One or more aspects of the invention can provide potable drinking waterthat meets or exceeds World Health Organization guidelines, that can beproduced from typical seawater feed with a total energy consumption ofbelow 1.5 kWh/m³ of water produced. Other aspects of the invention canbe directed to a combined electrodialysis and continuouselectrodeionization system and device and novel continuouselectrodeionization configuration that utilize concentration differencesto facilitate ion separation.

Some embodiments of the invention can involve multiple step processesutilizing electrodialysis (ED) devices to desalinate seawater to a totaldissolved solids (TDS) concentration, or salt concentration, in a rangeof about 3,500 to about 5500 ppm, followed by ion exchange (IX)softening, and final desalination to a TDS level of less than about1,000 ppm salt content by a novel version of continuouselectrodeionization (CEDI).

Our systems and processes of the present invention can involve a uniquecombination of existing and novel technologies, wherein each componentthereof utilized for reducing, or even minimizing, overall energyconsumption by advantageous use synergies between the differentcomponents and unit operations that aggregately overcomes respectivelimitations of current ED and CEDI devices. For example, because theenergy efficiency of ED devices typically decreases as the product TDSlevel is reduced below 5500 ppm, typically because of concentrationpolarization and water splitting phenomena, CEDI devices can be usedinstead to further desalt water containing such low TDS levels, lessthan 5500 ppm, at higher comparative efficiency because the latterdevice utilize ion exchange resin. To address scaling concerns, asoftener removes or reduces the concentration of non-monovalent,scale-forming species. The use of monovalent selective membranes in, forexample, a second, parallel electrodialysis train, can be used togenerate a regenerating stream for the softening stage, which typicallyhas a high concentration of monovalent species, thereby at leastreducing, if not eliminating any need for external salt stream storage.Further advantages can include improved water recovery.

Some further aspects of the invention can involve ED and CEDI devicesthat can be operated at sufficiently low current densities so thatconcentration polarization and water splitting are limited, whichreduces power demand.

The seawater desalination system, for example, can comprise a firsttreatment stage that preferably reduces a concentration of dissolvedspecies such as one or more dissolved solids. Some particular aspects ofthe present invention will be described with reference to seawater. Theinvention, however, is not limited to treating or desalinating seawaterand one or more principles thereof can be utilized to treat a liquidhaving target species to be removed therefrom.

One or more aspects of the invention can be directed to anelectrodeionization device comprising a first depleting compartmentfluidly connected to a source of water having dissolved solids therein,the depleting compartment defined at least partially by a cationicselective membrane and a first anionic selective membrane; a firstconcentrating compartment fluidly connected downstream from a source ofa first aqueous liquid having a first dissolved solids concentration,and in ionic communication with the first depleting compartment throughthe cationic selective membrane; and a second depleting compartmentfluidly connected downstream from a source of a second aqueous liquidhaving a second dissolved solids concentration that is greater than thefirst dissolved solid concentration, and in ionic communication with thefirst concentrating compartment through a second anionic selectivemembrane.

In some embodiments of the invention, the first aqueous liquid isseawater, typically having a first dissolved solids concentration ofless than about 4 wt %, typically about 3.3 wt % to 3.7 wt % and, insome cases, the second aqueous liquid is brine having a second dissolvedsolids concentration of at least about 10 wt %. In one or more furtherparticular embodiments, the first depleting compartment is fluidlyconnected to a source of water having a dissolved solids concentrationof less than about 2,500 ppm, or a ratio of the second dissolved solidsconcentration to the first dissolved solids concentration is at leastabout 3.

One or more aspects of the invention can be directed to devices fortreating water having dissolved ionic species therein. The device cancomprise, in some embodiments, a first depleting compartment fluidlyconnected to a source of the water, and at least partially defined by afirst anion selective membrane and a first cation selective membrane; afirst concentrating compartment fluidly connected to a source of a firstaqueous solution having a first concentration of dissolved solids, thefirst concentrating compartment in ionic communication with the firstdepleting compartment through one of the first anion selective membraneand the first cation selective membrane; and a second depletingcompartment fluidly connected to a source of a second aqueous solutionhaving a second concentration of dissolved solids that is greater thanthe first concentration of dissolved solids, wherein the seconddepleting compartment is typically in ionic communication with the firstconcentrating compartment through one of a second cation selectivemembrane and a second anion selective membrane.

In some embodiments of the invention, the device can further comprise asecond concentrating compartment fluidly connected at least one of asource of a third aqueous solution having a third concentration ofdissolved solids that is less than the second concentration of dissolvedsolids and the source of the first aqueous solution, the secondconcentrating compartment in ionic communication with the seconddepleting compartment through one of the second anion selective membraneand the second cation selective membrane. The second concentratingcompartment can, but not necessarily, be ionic communication with thefirst depleting compartment through the first cation selective membrane.In further configurations in accordance with some aspects of theinvention, the device comprises one or more salt bridges that, forexample, ionically connect the first depleting compartment and thesecond concentrating compartment. In other further embodiments of theinvention, the device can further comprise a third depleting compartmentfluidly connected to at least one of the source of the second aqueoussolution and a source of a fourth aqueous solution having a fourthconcentration of dissolved solids that is greater than the thirdconcentration of dissolved solids, wherein the third depletingcompartment is typically in ionic communication with the secondconcentrating compartment through a third cation selective membrane. Thedevice can further comprise a third concentrating compartment fluidlyconnected to at least one of a source of the first aqueous solution, thesource of the third aqueous solution, and a source of a fifth aqueoussolution having a fifth concentration of dissolved solids that is lessthan any of the second concentration of dissolved solids and the fourthconcentration of dissolved solids, the third concentrating compartmentin ionic communication with the third depleting compartment through athird anion selective membrane. The third concentrating compartment canbe in ionic communication with the first depleting compartment throughthe first cation selective membrane and, in some cases, the thirdconcentrating compartment is in ionic communication with the firstdepleting compartment through a salt bridge. Thus, in someconfigurations, the device has no electrodes or structures that providesexternal electromotive potential through the compartments thereof.

In other configurations of the device, the first depleting compartmentand the first concentrating compartment are fluidly connected downstreamfrom the same source.

One or more aspects of the invention can be directed to a seawaterdesalination system. The desalination system can comprise at least onefirst electrodialysis device including at least one first depletioncompartment having a first depletion compartment inlet fluidly connectedto a source of seawater, and a first depletion compartment outlet, andat least one first concentration compartment having a first depletioncompartment inlet and a first depletion compartment outlet; at least onesecond electrodialysis device including at least one second depletioncompartment having a second depletion compartment inlet fluidlyconnected to the source of seawater, and a second depletion compartmentoutlet, and at least one second concentration compartment having asecond concentration compartment inlet fluidly connected to the sourceof seawater, and a brine outlet; at least one ion exchanging unit havingan ion exchanger inlet fluidly connected to at least one of the firstdepletion compartment outlet and the second depletion compartmentoutlet, and an ion exchanger outlet; and at least oneelectrodeionization device having a first depleting compartment fluidlyconnected to the ion exchanger outlet, the depleting compartment can bedefined at least partially by a first cationic selective membrane and afirst anionic selective membrane, a first concentrating compartmentfluidly connected to the source of seawater, and in ionic communicationwith the first depleting compartment through the first cationicselective membrane, and a second depleting compartment fluidly connecteddownstream from the brine outlet, and in ionic communication with thefirst concentrating compartment through a second anionic selectivemembrane.

In one or more embodiments of the desalination system, at least one ofthe first concentrating compartment and the second depleting compartmentdoes not contain ion exchange resin.

In other configurations of the desalination system, the at least oneelectrodeionization device further comprises a second concentratingcompartment at least partially defined by the first anionic selectivemembrane, and having an inlet fluidly connected to the source ofseawater, and a third depleting compartment in ionic communication withthe second concentrating compartment through a second cationic selectivemembrane, and having an inlet fluidly connected to at least one of thebrine outlet, an outlet of the first concentrating compartment, and anoutlet of the second depleting compartment. In some cases, at least oneof the first concentrating compartment, the second depletingcompartment, the second concentrating compartment, and the thirddepleting compartment does not contain ion exchange resin.

The seawater desalination system, in some advantageous configurations,can further comprise one or more brine storage tanks, one or more ofwhich can be fluidly connected to at least one of an outlet of the firstconcentrating compartment and an outlet of the second depletingcompartment. One or more of the brine storage tanks can respectivelycomprise an outlet, any one or more of which can be fluidly connected toor connectable to the at least one ion exchanging unit, exclusively orto other unit operations of the desalination system.

In other configurations, the seawater desalination system can furthercomprise a third electrodialysis device having a third depletioncompartment fluidly connected downstream from the first depletioncompartment and upstream of the ion exchanging unit. Furtherconfigurations can involve systems that comprise a fourthelectrodialysis device having a fourth depletion compartment fluidlyconnected downstream from the second depletion compartment and upstreamof the ion exchanging unit.

In some advantageous configurations of the system, the at least onefirst electrodialysis device comprises a monovalent selective membranedisposed between the at least one first depletion compartment and the atleast one first depletion compartment. Further, the first depletingcompartment of the electrodeionization device can contain a mixed bed ofion exchange media, such as ion exchange resin.

Some further aspects of the invention can involve pre-treating water,preferably seawater or brackish water. In one or more configurations ofthe invention, the desalination system can further comprise at least onepretreatment unit operation which can be fluidly connected downstreamfrom the source of water to be treated, which can be seawater, orbrackish water, and, preferably, be fluidly connected, or connectable,upstream of at least one of the at least one first electrodialysisdevice, the at least one second electrodialysis device, and the at leastone electrodeionization device. The at least one pretreatment unitoperation can comprise at least one subsystem selected from the groupconsisting of a filtration system, a chlorination system, and adechlorination system. The pretreatment unit operation can comprise, insome configurations of the system, at least one of a microfilter, a sandfilter, and particulate filter.

In some cases, the pretreatment system can also comprise apressure-driven system that selectively removes divalent species such assulfate. For example, a nanofiltration system utilizing a FILMTEC™membrane, from The Dow Chemical Company, Midland, Mich., can be used toreduce the concentration of at least the sulfate species, which shouldfurther reduce the power consumption by one or more downstream unitoperations, such as any of the electrodialysis devices, and theelectrodeionization devices.

In still other configurations of one or more of the systems of theinvention, the at least one of the at least one electrodeionizationdevice comprises an anionic species collector, a cationic speciescollector, and a salt bridge in ionic communication with the anodic andthe cathodic collectors. The ionic species collectors can becompartments at least partially defined by ion selective media. Whenadvantageous, at least one of the at least one electrodeionizationdevice, the at least one first electrodialysis device, and the at leastone second electrodialysis device comprises an anode compartment fluidlyconnected downstream from a source of an aqueous solution havingdissolved chloride species, the electrode compartment comprising one ofa chlorine outlet and hypochlorite outlet. Further configurations caninvolve at least one of the at least one the electrodeionization device,the at least one first electrodialysis device, and the at least onesecond electrodialysis device comprising a second electrode compartmentcomprising a caustic stream outlet.

One or more aspects of the invention can involve a desalination systemcomprising a source of water which can at least partially have or beseawater; a means for selectively reducing a concentration ofmonoselective species in a first seawater stream to produce a firstdiluted stream; a means for increasing a dissolved solids concentrationin a second seawater stream to produce a brine stream; a means forexchanging at least a portion of divalent species for monovalent speciesin the first diluted stream, wherein the means for exchanging can have asecond diluted stream outlet; and an electrochemical separation device.The electrochemical separation device typically has a depletingcompartment fluidly connected to the second diluted stream outlet, and ameans for providing a concentration-induced electrical potential inionic communication with the depleting compartment.

In some configurations of the desalination system, the means forincreasing a dissolved solids concentration in the first seawater streamcomprises an electrodialysis device having a depletion compartmentfluidly connected to the source of seawater, and a concentrationcompartment separated from the depletion compartment by a monovalentselective membrane. The means for increasing a dissolved solidsconcentration in the second seawater stream can comprise anelectrodialysis device having a concentration compartment fluidlyconnected to the source of seawater, and a brine outlet providing thebrine stream. The means for providing a concentration-induced electricalpotential can comprise a first half-cell compartment fluidly connectedto a source of a first half-cell feed stream having a firstconcentration of total dissolved solids, and a second half-cellcompartment fluidly connected to a source of a second half-cell feedstream having a second concentration of total dissolved solids that isgreater than the first concentration of total dissolved solids. Thefirst half-cell compartment is typically fluidly connected to a sourceof seawater and the second half-cell compartment is fluidly connected toa source of brine.

One or more further aspects of the invention can be directed to anelectrodeionization device comprising a depleting compartment fluidlyconnected to a source of water having dissolved solids therein, thedepleting compartment defined at least partially by a cationic selectivemembrane and a first anionic selective membrane; and at least oneconcentration half-cell pairs in ionic communication with the depletingcompartment. The concentration half-cell pair typically comprises afirst half-cell compartment fluidly connected to a source of a firstaqueous liquid having a first dissolved solids concentration, and inionic communication with the depleting compartment through one of thecationic selective membrane and the first anionic selective membrane,and a second half-cell compartment fluidly connected downstream from asource of a second aqueous liquid having a second dissolved solidsconcentration that is greater than the first dissolved solidconcentration, and in ionic communication with the first half-cellcompartment through a second anionic selective membrane.

In some configurations of the electrodeionization device, the firstaqueous liquid is seawater. The second aqueous liquid can be a brinestream having a second dissolved solids concentration of at least about10 wt %. Thus, in some embodiments of the invention, the seconddissolved solids concentration to the first dissolved solidsconcentration is in a concentration ratio that is at least about three.

One or more still further aspects of the invention can be directed to amethod of desalinating seawater comprising reducing a concentration ofmonovalent species of seawater in a first desalting stage to producepartially desalted water; producing a brine solution from seawater, thebrine solution having a total dissolved solids concentration that is atleast twice the concentration of total dissolved solids in seawater;introducing the partially desalted water into a depleting compartment ofan electrically-driven separation device; and creating aconcentration-induced electrical potential in a concentration cell pairof the electrically-driven separation device while promoting transportof at least a portion of dissolved species from the partially desaltedwater in the depleting compartment into a compartment of theconcentration cell pair. The method can further comprise passing atleast a portion of the seawater through a nanofiltration system beforereducing the concentration of monovalent species of seawater in thefirst desalting stage.

The method can further comprise, in some approaches, replacing at leasta portion of dissolved non-monovalent species in the partially desaltedwater with dissolved monovalent species. Reducing the concentration ofthe monovalent species of seawater can involve selectively reducing theconcentration of dissolved monovalent species in an electrodialysisdevice. Producing the brine solution can involve promoting transport ofat least a portion of dissolved species from the seawater into a secondseawater stream flowing in a concentration compartment of anelectrodialysis device. The method of desalinating water can furthercomprise electrolytically generating one of chlorine and a hypochloritespecies in an electrode compartment, typically the anode compartment, ofat least one of an electrolytic device, an electrodialysis device andthe electrically-driven separation device, and electrolyticallygenerating a caustic stream in one or more compartments of at least oneof the electrolytic device, the electrodialysis device, and theelectrically-driven separation device. Further, the desalination methodcan also comprise at least partially disinfecting at least a portion ofthe seawater with the generated chlorine, the generated hypochloritespecies, or both.

Some particular aspects, embodiments, and configurations of the systemsand techniques of the invention can involve treating water in a system100 as exemplarily illustrated in FIG. 1.

The treatment system 100 can be fluidly connected or connectable to asource of a liquid to be treated 110. Typically, the liquid to betreated has mobile ionic species. For example, the liquid to be treatedcan be or comprise water having salts as dissolved solids therein. Inparticular applications of the invention, the liquid to be treated canbe seawater, comprise seawater, or consist essentially of seawater. Inother cases, the liquid to be treated can be brackish water, comprisebrackish water, or consist essentially of brackish water.

The treatment system 100 can comprise a first treatment stage 120fluidly connected to the source of liquid to be treated 110. Thetreatment system 100 can further comprise a second stage 130, and whereadvantageous, a third treatment stage 140 to produce treated product toa point of use 190.

The first treatment stage modifies at least one property orcharacteristic of the liquid to be treated. Preferably, the firsttreatment stage 120 reduces at least a portion of one or more targetspecies in the liquid to be treated to provide an at least partiallytreated liquid. For example, the first treatment stage 120 can utilizeone or more unit operations that remove at least a portion of dissolvedspecies in seawater from source 110 to produce at least a partiallytreated water or water stream 121 having a salinity content less thanseawater. Preferred configurations can provide at least partiallytreated water stream 121 that has at least 5% less salinity thatseawater from source 110. Other preferred configurations can provide theat least partially treated water that has at least 10% less salinitythat seawater. The first treatment stage 120 can utilize or be designedto provide a target change or difference in relative concentration orsalinity between the liquid to be treated, e.g., seawater, and the atleast partially treated liquid stream, e.g., at least partially treatedwater. The target difference in concentration provided by the firsttreatment stage 120 can be at least partially dependent on severalfactors or conditions including, but not limited to, any one or more ofthe capacity of one or more downstream unit operations, one or morerequirements of one or more of the downstream unit operations, and, insome case, the overall water demand of the treatment system 100. Forexample, the change in concentration, e.g., change in salinity, providedby the first treatment stage 120 can be dependent on desalinatingseawater to provide at least partially treated water that is conduciveto treatment by an electrodeionization device, a nanofiltration deviceor both. Other factors that may affect the design approach of the firsttreatment stage 120 can be dictated, at least partially, by economic oroperating considerations. For example, the first treatment stage 120 canbe configured to provide at least partially treated water utilizingavailable electrical power at an existing facility.

Further configurations or alternatives of the first treatment stage 120can involve one or more unit operations that selectively remove one ormore target or predetermined species from the liquid to be treated. Forexample, the first treatment stage can comprise or utilize one or moreunit operations that at least partially selectively remove from orreduce the concentration of dissolved monovalent species in the liquidto be treated. In other cases, the first treatment stage can comprise orutilize one or more unit operations that provide a product stream havinga concentration of one or more types of dissolved species therein thatis greater than the concentration of the dissolved species in the liquidto be treated. In still other cases, the first treatment stage canprovide a second product stream 123 having a concentration of dissolvedsolids therein that is greater than ancillary liquid stream, which canbe a stream from a unit operation that is unassociated with a unitoperation of treatment system 100. For example, the ancillary stream canbe a downstream byproduct of one or more sources (not shown). In othercases, the change in concentration or salinity provided by the firsttreatment stage 120 in the at least partially treated stream 102 can bedependent on providing a second product stream 123 that would beutilizable in one or more downstream unit operations of treatment system100. In still other cases, the first treatment stage 120 can provide asecond product stream 123 having a salinity that is greater than thesalinity of seawater, which has a typically salinity of about 3.5%.Preferably, the salinity of second product stream 123 is at least about5% but some particular embodiments of the invention can involve aproduct stream 123 having a salinity of at least about 9%. For example,the second product stream 123 can be a brine stream with a dissolvedsolids concentration of at least about 10%, or at least about 99,000ppm. In other exemplary embodiments, a ratio of the dissolved solidsconcentration in second product stream 123 to one or more other processstreams of treatment system 100 can be at least about 3, preferably, atleast about 5, and, in some advantageous cases which, for example, mayrequire a concentration difference or gradient, at least about 10.

The second stage 130 can have at least one unit operation that furthertreats the at least partially treated product stream 121. In someembodiments of the invention, the second stage 130 can comprise one ormore unit operation that adjusts one or more characteristics of the atleast partially treated stream 121 from the first stage 120 to provide asecond at least partially treated product stream or modified liquid 131.Preferably, the second stage 130 modifies at least two characteristicsof the stream 121 to produce stream 131.

The third treatment stage 140 can modify one or more properties orcharacteristics of one or more inlet streams thereinto. In particularlyadvantageous configurations in accordance with one or more aspects ofthe invention, the third treatment stage 140 can comprise one or moreunit operations that utilize at least one stream from at least oneupstream unit operation to modify another stream from one or moreupstream unit operations to provide a product stream to the point of use190 with at least one desirable property or characteristic. Furtherparticular configurations of the third treatment stage 140 can involveone or more unit operations that create a potential difference thatfacilitates treatment of the at least partially treated stream 131 toproduce a product stream 141. In still further preferred configurationsthe third treatment stage can produce another product stream 142 thatcan be utilize in one or more upstream unit operations of treatmentsystem 100. For example, the another product stream 142 can be abyproduct or second product stream utilized by one or more unitoperations of second stage 130 in, for example, a step or an operationthereof, as an inlet stream that at least partially facilitatesconversion of the at least partially treated stream 121 to provide theproduct stream 131 with at least one desirable property orcharacteristic. Further preferred embodiments or configurations of thirdtreatment stage 140 can involve unit operations that rely on adifference of a property or characteristic of the liquid to be treatedrelative to the property or characteristic the product stream from theunassociated unit operation or an upstream stage or unit operation oftreatment system 100 to at least partially facilitate treatment toprovide the product stream 141. For example, the third treatment stage140 can utilize the difference in salinity of seawater from the source110, as stream 111, relative to the salinity of stream 122 to at leastpartially facilitate reducing a concentration of one or more targetspecies in stream 131 to produce a product water 141 having at least onedesired characteristic, e.g., purity.

FIG. 2 illustrates an exemplary water treatment system 200 in accordancewith one or more aspects of the invention. The treatment system 200 cancomprise a first treatment stage including a first unit operation 220and a second unit operation 222, each preferably, but not necessarilyfluidly connected to the source 110 of water to be treated throughrespective inlets thereof. The treatment system 200 further comprises asecond stage 230 fluidly connected to receive, typically at an inletthereof, one or each product stream from the first unit operation 220and the second unit operation 222, typically from respective outletsthereof. The treatment system 200 can further comprise a third treatmentstage 240 having an inlet fluidly connected to at least one of an outletof the second stage 230, an outlet of one or more unit operations of thefirst treatment stage, the source of water to be treated, and theunassociated unit operation, to provide a product water to, for example,the point of use or a storage 190.

As illustrated in the exemplary embodiment of FIG. 2, the first unitoperation 220 can provide a first partially treated water stream and becombined with another at least partially treated water stream from unitoperation 222 to produce an at partially treated product stream 221. Thefirst water stream from an outlet of unit 220 can have one or morecharacteristics that differ from those of the second water stream fromunit 222. The first and second unit operations are preferably designedto provide the at least partially treated water stream 221 having atleast one target property for further modification or treatment insecond stage 230. The second unit operation 222 can provide a secondproduct stream 223, which preferably has one or more particular ortarget characteristics. Thus, some configurations of the inventioncontemplate unit operations 220 and 222 that collectively provide an atleast partially treated water stream 221 with one or more particularcharacteristics while further providing a second product aqueous stream223 with one or more characteristics that typically differ from thecharacteristics of stream 221. The first treatment stage can utilizewater treating unit operations, devices, or systems such as, but notlimited to electrodialysis devices and electrodeionization devices.

Further particular embodiments of the invention can involve a first unitoperation that is operated to have lower power consumption relative tothe second unit operation. The first unit operation 220 can be operatedto produce from seawater, an at least partially treated water product orstream having a total dissolved solids of about 2,500 ppm, with about30% water recovery. The second unit operation 222 can be operated toproduce from seawater, an about 10% brine solution having a dissolvedsolids concentration of greater than about 99,000 ppm.

In another embodiment (not shown), the second stage 130 can comprise twoor more unit operations that separately receive streams from the firstand second unit operations 220 and 222. One or more preferredconfigurations of the second stage 230 can involve one or more unitoperations that alter at least one property of inlet stream 221 from atleast one unit operation of the first treatment stage. The second stagecan thus provide a third product stream 231, with one or more targetcharacteristics, and which can be further treated in the third treatmentstage 240.

Other embodiments of the invention can involve ion exchanging unitscomprising chloride-form anion exchanging resin that exchange at least aportion of sulfate species in favor of chloride species to furtherreduce power requirements of one or more downstream unit operations,and, in some cases, to further reduce the likelihood of scale formationin such downstream unit operations. Thus, the exchanging unit caninvolve cation exchanging resin that at least partially reduces theconcentration of non-monovalent cationic species, such as Ca⁺ and Mg⁺,in favor of monovalent cation species, such as Na⁺, and, preferably,further comprises anion exchanging resin that at least partially reducesthe concentration of non-monovalent anionic species, such as SO₄ ²⁻, infavor of monovalent anionic species, such as Cl⁻, which can reduce thetreatment power requirement of one or more downstream unit operations.Regeneration of any of the ion exchanging resin types can be performedwith, for example, a waste brine stream having dissolve Na⁺ and Cl⁻.

The third treatment stage 240 can comprise one or more unit operationsthat utilize the second product water or aqueous stream 223 and anotherstream, such as a water stream 111 from source 110 to facilitatetreatment of the third water product stream 231 and provide treated,product water to the point of use or storage 190. Further preferredconfigurations of the third treatment stage 240 can involve producing abyproduct water or aqueous stream 241, which can be used in one or moreupstream or downstream stages of the treatment system 200. For example,the byproduct water stream can be used in one or more unit operations inthe second stage 230 as an input or reactant during operation thereof.The third treatment stage can utilize one or more unit operations,devices, or systems such as, but not limited to electrodialysis andelectrodeionization devices.

FIG. 3 illustrates a seawater desalination system 300 in accordance withone or more aspects of the invention. Desalination system 300 typicallycomprises a first train having at least one first electrodialysis device321A and, preferably, at least one second electrodialysis device 322B.Desalination system 300 can further comprise a second train having atleast one third electrodialysis device 323A and, preferably, a secondelectrodialysis device 324B. Desalination system 300 can also compriseat least one ion exchanging subsystem 330 with at least one ionexchanger inlet in fluid communication with an outlet of at least one ofthe upstream electrodialysis devices 321A, 322B, 323A, and 324B.Desalination system 300 can also comprise a third treatment stage 340that can further treat the at least partially treated water 331 from atleast one ion exchanger outlet of ion exchanging subsystem 330.

The first electrodialysis device 321A has at least one depletioncompartment 321D1 having an inlet fluidly connected to a source 310 ofseawater. The first electrodialysis device 321A also comprises at leastone concentration compartment 321C1, preferably fluidly connected to thesource 310 of seawater. The second electrodialysis device 322B of thefirst train typically comprises at least one depletion compartment 322D2and at least one concentration compartment 322C2. An outlet of the firstdepletion compartment 321D1 is fluidly connected to at least one of aninlet of the at least one depletion compartment 322D2 and an inlet ofthe at least one concentration compartment 322C2 of the secondelectrodialysis device 322B. In some particular embodiments, the inletof the at least one concentration compartment 322C2 of the secondelectrodialysis device 322B is fluidly connected to the source 310 ofseawater. Preferred embodiments in accordance with some aspects of theinvention involve a first train of devices that at least partiallytreats seawater to produce an at least partially treated water 321having at least one target characteristic. For example, the first trainof electrodialysis devices that partially desalinate water, preferably,selectively removes dissolved solids species from the seawater, toproduce an at least partially treated product water stream 321 havingany one or more of a dissolved solids concentration that is less thanseawater, relatively higher ratio of dissolved non-monovalent dissolvedsolids species to dissolved monovalent species than the correspondingratio of seawater, and a lower concentration of dissolved monovalentspecies concentration. In embodiments that seek to selectively removedissolved monovalent species, one or more monovalent selective membranescan be used to define, at least partially the depletion compartments,and, preferably, at least partially define a concentration compartment.For example, the electrodialysis device 321A can have a first depletioncompartment 321D1 at least partially defined by a monovalent anionicselective membrane 381 and a monovalent cationic selective membrane (notshown), and a first concentration compartment 321C1 in ioniccommunication with the first depletion compartment through themonovalent anionic selective membrane 381, and, optionally, a secondconcentration compartment (not shown) through the monovalent cationicselective membrane. The second electrodialysis device 322B can also beoptionally configured to have one or more monovalent selective membranesthat facilitate selective removal or depletion one or more monovalentspecies from the water stream introduced into the depletion compartmentsthereof and accumulated into the concentration compartments thereof.

During operation of the first and second electrodialysis devices,seawater can be used as a concentration stream, feeding into theconcentration compartments 321C1 and 322C2, which collects the one ormore removed species from the streams introduced into the depletioncompartments. The concentration streams leaving compartments 321C1 and322C2 and containing species removed from the depletion compartments canbe discharged as a waste or reject stream or be utilized in otherunassociated processes R.

The at least one third electrodialysis device 323A can be configured toprovide a product stream that is useable in a downstream unit operationof desalination system 300. In accordance with a particular embodiment,the third electrodialysis device 323A can have at least one depletioncompartment 323D1 and at least one concentration compartment 323C1 inionic communication with at least one of the depletion compartments323D1 through a ion selective membrane 382. Preferably, an electriccurrent applied through the third electrodialysis device 323A providesufficient potential to provide a product water stream from theconcentration compartment 323C1 having one or more predetermined ortarget characteristics. For example, electrodialysis device 323A canalso be constructed with a monovalent selective membrane that separatesbut provides ionic communication between the depletion compartment 323D1and the concentration compartment 323C1. The at least one fourthelectrodialysis device 324B can comprise at least one depletioncompartments 324D2, defined at least partially by anionic and cationicselective membranes, and at least one concentration compartment 324C2,typically in ionic communication with at least one of a depletioncompartment 324D2. During operation of system 300, product water fromthe depletion compartment 323D1 can be introduced into the depletioncompartment 324B to further treat seawater from source 310 andfacilitate production of at least partially treated water 221. Asexemplarily illustrated, the product water from the depletioncompartment 324D2 can be combined with product water 321 from thedepletion compartment 322D2 to produce the at least partially treatedwater 221 for further treatment.

The first train including the first and second electrodialysis devices321A and 322B can be operated to produce water having a target totaldissolved solids concentration, such as about 2,500 ppm, with an overallwater recovery rate of about 30%. The first and second electrodialysisdevices 321A and 322B can utilize at least one of monovalent anionselective membrane and cation selective membrane and, preferably, atleast the first electrodialysis device 321A utilizes monovalent anionselective membranes and monovalent selective cation selective membrane,which should at least reduce any scaling potential therein.

The second train including the third and fourth electrodialysis devices323A and 324A can be operated to produce a brine stream having a targetsalinity content of at least about 10% (NaCl) in a concentrate streamfrom one or more concentration compartments thereof. Preferably, thethird electrodialysis device produces a sufficient amount of brine at atleast the target salinity level while operating at a water recovery ofabout 70%. The fourth electrodialysis device 324B can be operated toproduce the at least partially treated water having a target dissolvedsolids content of about 2,500 ppm, and preferably with a recovery rateof about 48%. In some particular configurations of the invention, theoverall recovery rate of the second train can be about 40%.

The ion exchanging subsystem 330 can be configured to receive at least aportion of the at least partially treated water 221 and convert ormodify at least one characteristic thereof. Some embodiments of one ormore aspects of the invention involve selectively reducing aconcentration of a target dissolved species of a water to be treatedwhile at least partially retaining or inhibiting transport of at least aportion of non-target or other dissolved species, and then substitutingat least a portion of the retained dissolved species with the targetdissolved species. For example, water 221 can have a relative highconcentration of non-monovalent dissolved species, such as calcium andmagnesium, compared to seawater, and be treated to exchange at least aportion of the non-monovalent species for monovalent species, such assodium. Some configurations of the exchanging subsystem 330 can involveat least two exchange trains (not shown) of softeners or beds of ionexchange media. The first ion exchange train can comprise a leading ionexchange bed followed by a lagging ion exchange bed, which canpreferably substitute at least a portion of the non-monovalent dissolvedspecies in the water, such as Ca⁺ and Mg⁺, in favor of monovalentdissolved species such as Na⁺. The second ion exchange train cansimilarly comprise serial leading and lagging ion exchange beds. Duringoperation, the one of the first and second ion exchange trains can havean inlet fluidly connected to receive at least a portion of at leastpartially treated water 221 and produce an exchange water stream havingless non-monovalent dissolved species concentration. Once the first ionexchange train becomes saturated with non-monovalent species as a resultof the non-monovalent for monovalent ion exchanging process, the secondion exchange train can be utilized. The first train can then beregenerated by introducing an aqueous stream rich in monovalentdissolved species to replace at least a portion of non-monovalentspecies bound to the ion exchange media of the ion exchange beds. Theion exchange units can comprise a mixed bed of ion exchange resin suchas those commercially available as AMBERLITE™ and AMBERJET™ resin fromRohm and Haas, Philadelphia, Pa.

Regeneration of the ion exchange media can be performed by utilizing abrine solution 261 with sufficient salinity, such as about 10%, from abrine storage tank 260. A discharge stream 332 from ion exchangingsubsystem 330 can be discharged as a reject stream. Salinity sufficientto regenerate the ion exchange media can be at a level that surpassesthe thermodynamic resistance associated with binding the non-monovalentspecies to the exchange matrix.

The third treatment stage 340 can comprise one or moreelectrodeionization device. In some embodiments of the invention, thethird treatment stage can comprise at least one of a conventionalelectrodeionization device as illustrated in FIG. 4 and a modifiedelectrodeionization device as illustrated in FIG. 5. In still otherconfigurations in accordance with one or more aspects of the invention,the third treatment stage can comprise one or more electrodelesscontinuous deionization devices.

The electrodeionization device illustrated in FIG. 4 typically comprisesat least one depleting compartment 411 and at least one concentratingcompartment 412, disposed adjacent at least one of the depletingcompartment 411. Each of the depleting and concentrating compartmentsare at least partially defined by any of an anion selective membrane AEMand a cation selective membrane CEM. In contrast to electrodialysisdevices, the compartments of electrodeionization device contain cationexchange resin and anion exchange resin. During operation with animposed electrical current, cationic species, such as Na⁺, typicallymigrate to a cathode (−) of the device and anionic species, such Cl⁻,typically migrate toward an anode (+) of the device 400. The anionselective membrane AEM and the cation selective membranes CEM trap themigrating or transporting dissolved species, Na⁺ and Cl⁻, in respectiveconcentrating compartments 412 as reject streams R. The feed into one ormore of the depleting compartments is typically the softened waterstream 331 from the ion exchanging subsystem 330. The product water fromthe depleting compartments can then be stored or delivered to a pointuse. One or more power supplies (not shown) typically provideselectrical energy or power to the electrodeionization device 400 thatfacilitates separation of the target dissolved species. In some cases, aportion of the electrical energy is utilized to dissociate water to H⁺and OH⁻ species. The power supply can be controlled to provide a desiredor target current level, desired or target voltage or potential level,and current polarity.

FIG. 5 exemplarily illustrates a modified electrodeionization device 500that can be utilized in the third treatment stage of the treatmentsystem. The device 500 comprises at least one first depletingcompartment 511, which is typically at least partially defined by afirst cation selective membrane 521C and a first anion selectivemembrane 531A at least one first concentrating compartment 521, and atleast one first concentrating compartment 541, which can be at leastpartially defined by a second anion selective membrane 532A, and inionic communication the first depleting compartment 511 through at leasta portion of the first cation selective membrane 521C. The device 500can further comprise a second depleting compartment 512, which isdefined at least partially by a second cation selective membrane 522C,and in ionic communication with the first concentrating compartment 541through at least a portion of the second anion selective membrane 532A.The electrodeionization device 500 can further comprise a secondconcentrating compartment 542 defined at least partially by a thirdcation selective membrane 523C. The second concentrating compartment 542is preferably at least partially in ionic communication with the firstdepleting compartment 511 through the first anion selective membrane531A. The electrodeionization device 500 can further comprise a thirddepleting compartment 513 preferably defined by a third anion selectivemembrane 533A. The third depleting compartment 513 is preferably atleast partially in ionic communication with the second concentratingcompartment 542 through the third cation selective membrane 523C. Theelectrodeionization device 500 typically has an anode compartment 562housing an anode, and a cathode compartment 564 housing a cathode.

In accordance with other aspects of the invention, theelectrodeionization device 500 comprises a first depleting compartment511 containing cation exchange media and anion exchange media such ascation exchange resin CX and anion exchange resin AX, and at leastpartially defined by the first cation selective membrane 521C and thefirst anion selective membrane. In some cases, only the first depletingcompartment or only the compartments receiving or fluidly connecteddownstream from any of the depletion compartments of the electrodialysisdevices and the ion exchange unit comprises electroactive media such asion exchange resin, and the other compartments are free of ion exchangemedia. For example, in some configurations of the electrodeionizationdevice 500, each of the one or more first depleting compartmentscomprises 511 a mixed bed of ion exchange resin, and each of the one ormore first concentrating compartments 541, the one or more seconddepleting compartments 512, the one or more second concentratingcompartments 542, and the one or more third depleting compartments 513do not contain ion exchange media.

In operation, power from a power supply (not shown) provides electricalenergy for an electric field, which is typically created across theelectrodeionization device 500 through the anode and the cathode. Waterto be treated from, for example, an outlet of second stage ionexchanging unit 330 enters the depleting compartment 511 through aninlet thereof. The water to be treated has dissolved species that canmigrate under the influence of the electric field in theelectrodeionization device 500. Typically, the aqueous stream 331contains a higher amount of target dissolved monovalent species, Na⁺ andCl−, relative to dissolved non-monovalent species because of the ionexchanging process in unit operation 330. Thus, because the amount ofenergy associated with promoting transport of monovalent species can berelatively less than the associated amount of energy in promotingtransport of non-monovalent species, additional capital and operatingcosts for second stage 330 can be reduced, if not eliminated. Themonovalent species typically migrate to the corresponding attractingelectrodes and further through the anion or cation selective membranesinto one of the first concentrating compartment and the secondconcentrating compartment. For example, cationic Na⁺ species can bedrawn to the direction of the cathode and typically pass through thecation selective membrane 521C whereas the anionic Cl⁻ species can bedrawn toward the anode and typically pass through the anion selectivemembrane 531A. The product stream from the outlet of the depletingcompartment 331 will typically have a reduced concentration of thetarget dissolved solids species.

In some configurations of the invention, a stream having a firstconcentration of dissolved solids therein can be used a concentratingstream to collect the migrating target dissolved solids species. Forexample, a seawater stream 111 having a salinity of about 3.5% can beused as the concentrating stream introduced into the first concentratingcompartment 541. The stream leaving the first concentrating compartment541 will thus be typically rich in the migrating cation or anionspecies. This stream can be discharged as waste or reject stream R. Alsoduring operation, another feed stream is typically introduced into thesecond depleting compartment 512 and the third depleting compartment513.

The electrodeionization device 500 can further comprise a firstconcentration cell pair 531 and, optionally, a second concentration cellpair 532, each of which is preferably in ionic communication with thefirst depleting compartment 511. The first concentration cell pair 531can comprise a first half-cell compartment 541 fluidly connected to asource of a first aqueous liquid having a first dissolved solidsconcentration, and in ionic communication with the depleting compartment511 through the first cationic selective membrane 521C, and a secondhalf-cell compartment 512. The second half-cell compartment is typicallyin ionic communication with the first half-cell compartment 541 throughthe anion selective membrane 532A. The optional second concentrationcell pair 532 can comprise a third half-cell compartment 542 and afourth half-cell compartment 513. The third half-cell compartment istypically in ionic communication with the depleting compartment 511through the anion selective membrane 531A. The fourth half-cell 513compartment is typically in ionic communication with the third half-cellcompartment 542 through the cation selective membrane 523C.

Further advantageous features of the invention can involve establishinga concentration difference between adjacent cell by providingcompositionally similar respective feed streams but with differingconcentrations of dissolved constituents. The concentration differencegenerates a potential, e.g., an electromotive potential E (in V), thatcan be at least partially quantified by the Nernst equation,

$E = \frac{{RT}\; \ln \left\lfloor \frac{\left( {{conc}\; 1} \right)}{\left( {{conc}\; 2} \right)} \right\rfloor}{n\; F}$

where conc1 is the concentration of dissolved solids in the stream 223introduced into the second half cell 512, conc2 is the concentration ofdissolved solids in the stream 111 introduced into the first half-cell541, R is the gas constant, 8.314 J/(Kmole), T is the temperature,typically 298 K, n is the number of electrons transferred in the cellreaction, n=1 for seawater and brine, and F is the Faraday constant,96,498 coulombs/mole. Thus, some preferred configurations in accordancewith some aspects of the invention can involve utilizing a brine stream223 having a dissolved solids concentration greater than the dissolvedconcentration of seawater stream 111 introduced into the first depletingcompartment. The brine stream, typically having a salinity of at leastabout 8%, preferably at least about 10%, and more preferably, at leastabout 12%, or a dissolved solids concentration of at least about 80,000ppm, preferably, at least about 99,400 ppm, and more preferably, atleast about 120,000 ppm can be used a feed stream 223 introduced intothe second half-cell compartment 512, and preferably also into thefourth half-cell compartment 513. Each of the streams 341 leaving thesecond and fourth half-cell compartments 512 and 513 may still have ahigh brine content, relative to seawater, and can be directed to storagein a brine storage tank 260. The feed stream 111 introduced into thefirst half-cell compartment 541, and optionally also the third half-cellcompartment 542, can be seawater or an aqueous stream having a salinityof about 3.5% or a dissolved solids concentration of less than about36,000 ppm. The above-noted exemplary conditions can provide about 0.026volts per concentration cell pair. Thus, the present invention canadvantageously generate electrical potential that facilitates treatmentor desalination of seawater. Example 1 below provides expected generatedpotentials based on exemplary conditions when utilizing a first streamand a second stream in a concentration cell pair, wherein the secondstream has a concentration of dissolved solids greater the concentrationof dissolved solids of the first stream.

In some cases, one or more devices of the third treatment stagecomprises sufficient number of concentration cell pairs to providesubstantially all the electrical potential required to desalinate theproduct stream 331 to a desired level. In such configuration, the devicecan comprise a salt bridge (not shown), typically having an electrolytetherein, such as potassium chloride or sodium chloride, that ionicallyconnects the half-cell compartments of the device. For example, a firstend of a salt bridge can ionically connect the second half-cellcompartment 512 with any of depleting compartment 511 and the fourthhalf-cell compartment 513.

FIGS. 6A and 6B illustrate electrodeless continuous deionization devices600 and 610 that may be characterized, in accordance with still someaspects of the invention, as being Donnan potential assisted or aDonnan-enhanced EDI device. The device 600 can comprise a circularcylindrical shell 601 housing at least one first depleting compartment611, each having liquid to be treated 331 introduced thereinto. Thedevice can further comprise at least one first concentrating compartment621, each having a first feed stream 111 introduced thereinto, and atleast one second depleting compartment 612, each having a second feedstream 223 introduced thereinto. The device 600 typically furthercomprises at least one second concentrating compartment 622, each havinga third feed stream 112 introduced thereinto. The first depletingcompartment 611 can be defined by an anion selective membrane 641A and acation selective membrane 651C. The first concentrating compartment 621can be defined by an anion selective membrane, such as membrane 641A,and a second cation selective membrane 652C. As exemplarily illustrated,the first depleting compartment is in ionic communication with the firstdepleting compartment through membrane 641A. The second depletingcompartment 612 can be defined by a cation selective membrane and secondanion selective membrane 642A. Preferably, the second depletingcompartment 612 is in ionic communication with the first concentratingcompartment 621 through cation selective membrane 652C. The secondconcentrating compartment 622 can be defined by an anion selectivemembrane and a cation selective membrane. Preferably, the secondconcentrating compartment is in ionic communication with the seconddepleting compartment 612 through the second anion selective membrane642A. Further preferred configurations can involve having the secondconcentrating compartment in ionic communication with the firstdepleting compartment 611 through one of a salt bridge and the firstcation selective membrane 651C. Member 661 can provide ionic andelectrical insulation as well as structural support for thecompartments.

The second feed stream 223 typically has a concentration of dissolvedsolids therein that is greater than the concentration of dissolvedsolids in the first feed stream 111, and preferably, also greater thanthe concentration of dissolved solids in the third feed stream 112. Theconcentrations of dissolved solids of each of the first feed stream andthe third feed stream can be the same or less than the concentration ofdissolved solids in the liquid to be treated 331. As described above,the concentration differences to between the paired half-cells 612 and621, and 612 and 622, can create a potential that facilitates transportof Na⁺ and Cl⁻ species from the depleting compartment 611, asillustrated, to produce the product stream.

Similar to the electrodeless device 600, the device 610 illustrated inFIG. 6B comprises a second cell pair including a depleting compartment613 and concentrating compartment 623, respectively having feed streams113 and 114. Feed stream 113 can be brine from, for example,electrodialysis device 323A, and feed stream 114 can be seawater fromthe source 310. A plurality of pairs of depleting and concentratingcompartments utilizing seawater and brine streams to advantageouslygenerate a potential sufficient to drive the treatment of at leastpartially treated water, having a dissolved solids concentration of, forexample, about 2,500 ppm, to produce product water having a targetdissolved solids concentration of, for example, about 500 ppm.

Other configurations can involve any one or more of the feed streams 111and 114 at least partially comprising at least partially treated water331, which can provide a greater concentration difference relative tobrine stream 223.

Further notable differences include countercurrent flow directions ofsome of the streams through the compartments. As illustrated, the secondstream 111 can be counter-currently introduced into the firstconcentrating compartment 621, relative to the direction of the streamintroduced into the first depleting compartment 611 or, in some cases,relative to the third stream 223 introduced into the second depletingcompartment. Concentration differences between the second and thirdstreams can create a potential driven by the half-cell reactionsassociated with migration of dissolved species, such as Na⁺ and Cl⁻.

Any of the membranes in devices 600 and 610 can be monovalent anionselective or monovalent cation selective.

In some configurations of the invention, an electrolytic device (notshown) can be used to generate an aqueous solution comprising adisinfecting species such as chlorine, chlorite, hypochlorite, andhypobromite. In other configurations, at least one of theelectrodeionization device and any one or more of the electrodialysisdevices can be utilized to generate any one or more of an acidicsolution, a basic solution, and a disinfecting solution. For example, arelatively pure water stream can be introduced into the anodecompartment (+) to collect and aggregate H⁺ species to produce an acidicoutlet stream having a pH of less than 7. A chloride containing solutioncan be introduced in a feed stream into the cathode compartment tofacilitate generation of a disinfecting species such as chlorine and ahypochlorite species. Gaseous hydrogen byproduct may be vented orotherwise discharged.

Any of the various subsystems, stages, trains, and unit operations ofthe invention can utilize one or more controllers to facilitate,monitor, and/or regulate operation thereof. Preferably, a controller(not shown) monitors and, in some cases, controls each of the componentsof the systems of the invention.

The controller may be implemented using one or more computer systems.The computer system may be, for example, a general-purpose computer suchas those based on an Intel PENTIUM®-type processor, a Motorola PowerPC®processor, a Sun UltraSPARC® processor, a Hewlett-Packard PA-RISC®processor, or any other type of processor or combinations thereof.Alternatively, the computer system may include specially programmed,special-purpose hardware, for example, an application-specificintegrated circuit ASIC or controllers intended for analytical systems.

The computer system can include one or more processors typicallyconnected to one or more memory devices, which can comprise, forexample, any one or more of a disk drive memory, a flash memory device,a RAM memory device, or other device for storing data. The memory deviceis typically used for storing programs and data during operation of thetreatment system and/or the computer system. For example, the memorydevice may be used for storing historical data relating to theparameters over a period of time, as well as operating data. Software,including programming code that implements embodiments of the invention,can be stored on a computer readable and/or writeable nonvolatilerecording medium, and then typically copied into the memory devicewherein it can then be executed by the processor. Such programming codemay be written in any of a plurality of programming languages, forexample, Java, Visual Basic, C, C#, or C++, Fortran, Pascal, Eiffel,Basic, COBAL, or any of a variety of combinations thereof.

Components of the computer system may be coupled by an interconnectionmechanism, which may include one or more busses, e.g., betweencomponents that are integrated within a same device and/or a networke.g., between components that reside on separate discrete devices. Theinterconnection mechanism typically enables communications e.g., data,instructions to be exchanged between components thereof.

The computer system can also include one or more input devices, forexample, a keyboard, mouse, trackball, microphone, touch screen, valves,position indicators, fluid sensors, temperature sensors, conductivitysensors, pH sensors, and composition analyzers, and one or more outputdevices, for example, a printing device, display screen, or speaker,actuators, power supplies, and valves. In addition, the computer systemmay contain one or more interfaces not shown that can connect thecomputer system to a communication network in addition or as analternative to the network that may be formed by one or more of thecomponents of the system.

According to one or more embodiments of the invention, the one or moreinput devices may include sensors for measuring one or more parametersof the treatment system. Alternatively, the sensors, the metering valvesand/or pumps, or all of these components may be connected to acommunication network that is operatively coupled to the computersystem. For example, sensors may be configured as input devices that aredirectly connected to the computer system, and metering valves and/orpumps may be configured as output devices that are connected to thecomputer system, and any one or more of the above may be coupled toanother computer system or component so as to communicate with thecomputer system over a communication network. Such a configurationpermits one sensor to be located at a significant distance from anothersensor or allow any sensor to be located at a significant distance fromany subsystem and/or the controller, while still providing datatherebetween.

The controller can include one or more computer storage media such asreadable and/or writeable nonvolatile recording medium in which signalscan be stored that define a program to be executed by the one or moreprocessors. The medium may, for example, be a disk or flash memory. Intypical operation, the one or more processors can cause data, such ascode that implements one or more embodiments of the invention, to beread from the storage medium into a memory structure that allows forfaster access to the information by the one or more processors than doesthe medium. The memory structure is typically a volatile, random accessmemory such as a dynamic random access memory DRAM or static memory SRAMor other suitable devices that facilitates information transfer to andfrom the processor.

Although the computer system is shown by way of example as one type ofcomputer system upon which various aspects of the invention may bepracticed, it should be appreciated that the invention is not limited tobeing implemented in software, or on the computer system as exemplarilyshown. Indeed, rather than implemented on, for example, a generalpurpose computer system, the controller, or components or subsectionsthereof, may alternatively be implemented as a dedicated system or as adedicated programmable logic controller PLC or in a distributed controlsystem. Further, it should be appreciated that one or more features oraspects of the invention may be implemented in software, hardware orfirmware, or any combination thereof. For example, one or more segmentsof an algorithm executable by the controller can be performed inseparate computers, which in turn, can be communication through one ormore networks.

EXAMPLES

The function and advantages of these and other embodiments of theinvention can be further understood from the examples below, whichillustrate the benefits and/or advantages of the one or more systems andtechniques of the invention but do not exemplify the full scope of theinvention.

Example 1

In this example, the expected potential that can be generated byutilizing concentration cell pairs in some configurations of the devicesof the invention. Table 1 below provides calculated potentials based onconcentrations of streams introduced into the half-cell compartmentsaccording to the Nernst equation at room temperature.

The table below shows that the ratio of concentrations of the feedstreams is preferably as large a possible to increase the generatedpotentials. For example, the concentration ratios can be at least about2, preferably at least about 3, more preferably at least about 5, andeven more preferably at least about 10.

TABLE 1 CONC1 CONC2 E (volts) E (mV) 1 1 0 0 10 1 0.059 59.1 100 1 0.118118.2 1,000 1 0.177 177.4 10,000 1 0.024 236.5 2 1 0.018 18.8 3 1 0.02828.2 4 1 0.036 35.6 5 1 0.041 41.3 6 1 0.046 46.0 7 1 0.050 50 8 1 0.05353.4 9 1 0.056 56.4 5.68 1 0.044 44.6 2.3 1 0.021 21.4

The following listing provides the ionic concentrations of typicalseawater. The predominant cationic species in seawater are Na⁺, K⁺, Ca²⁺and Mg²⁺, and the predominant anionic species are Cl⁻ and SO₄ ²⁻. Therespective concentrations of the bicarbonate and carbonate species willdepend on pH of the water.

Concentration Species (ppm) Chloride 19,353 Sodium 10,781 Sulfate 2,712Magnesium 1,284 Potassium 399 Calcium 412 Carbonate/bicarbonate 126Bromide 67 Strontium 7.9 Boron 4.5 Fluoride 1.28 Lithium 0.173 Iodide0.06 Barium less than 0.014 Iron less than 0.001 Manganese less than0.001 Chromium less than 0.001 Cobalt less than 0.001 Copper less than0.001 Nickel less than 0.001 Selenium less than 0.001 Vanadium less than0.002 Zinc less than 0.001 Molybdenum less than 0.01 Aluminum less than0.001 Lead less than 0.001 Arsenic less than 0.002 Cadmium less than0.001 Nitrate 1.8 Phosphate 0.2

Example 2

This example provides exemplarily electrodialysis trains that can beutilized in accordance with some aspects of the invention.

FIG. 10A exemplarily illustrates train of electrodialysis devices thatcan be used in the first train 220 of the first treatment stage. Train220 can comprise multiple stages, each operating at optimum voltage andcurrent density to minimize energy use. As illustrated, the train 220can have four stages of electrodialysis devices.

In the first train, the depletion compartment can be serially connectedand dilution streams are in series, with the product from one stageserving as a feed to downstream depletion compartments. Fresh seawateris used as feed to each of the associated concentrate compartments ineach stage to minimize any concentration difference between the diluteand concentrate compartments in each stage.

Each stage can also have a number of ED modules operating in parallel.

The second train 222 can also comprise multiple stages ofelectrodialysis devices, having serially connected depletioncompartments. The respective depletion compartments can also be seriallyconnected to increase the aggregate NaCl concentration in the brinestream therefrom to a salt content of about 10%. As illustrated in FIG.10B, the second train 222 can have four electrodialysis stages, each ofwhich preferably utilizes monovalent selective membranes.

The third train (not show) can also involve a plurality ofelectrodialysis stages to facilitate reducing the dissolved solidsconcentration of the water stream to be in a range of about 3,500 ppm toabout 5,500 ppm.

Example 3

This example describes expected performance of a system utilizing thetechniques of the invention as substantially represented in FIG. 3 witha device schematically illustrated in FIG. 4 for desalinating seawaterat a rate of about 8,000 m³/hr.

Two trains of electrodialysis (ED) device were simulated with finiteelement calculations with a softener and an electrodeionization (EDI)device. Several stages were used in the finite element simulation;stages 1-5 were designed to generate a brine stream with at least 10%NaCl; and the final two stages were designed to reduce the dissolvedsolids concentration of the product stream by the softener and theelectrodeionization device. Table 2 and 3A-3C below list the simulationparameters and calculated results. Table 4 summarizes the predictedenergy requirement for the ED/EDI system.

FIG. 7 graphically illustrates the expected energy required indesalinating seawater to produce product water of various targetcharacteristics.

The incoming sweater was assumed to have about 35,700 ppm totaldissolved solids (TDS) after being pretreated with a 10 micronprefiltration (not shown) using commercially available pretreatmentequipment. It is noted that extensive pretreatment, such as pretreatmenttypically associated with reverse osmosis systems is unnecessary forED/CEDI process of the present invention because the water is not forcedthrough the membrane in these processes.

The feed water is split into ED train 1, ED train 2 and a concentratestream (brine) from ED train 2 is configured to feed to the CEDI train.

ED train 1 is passed through two stages to optimize the powerutilization for each stage. Train 1 produces 2,500 ppm TDS qualityproduct at about a 30% recovery.

Standard electrodialysis modules are expected to be used in this train.The use of monovalent selective ion exchange membrane in stage 1 of thistrain should minimize the potential of scaling in the concentratecompartment.

ED train 2, stage 1 is designed to produce 10% NaCl (brine) solution inthe concentrate stream. The brine will be used to regenerate thesoftener downstream and as one of the concentrating stream in the CEDImodule. This Electrodialysis stage would utilize monovalent selectiveion exchange membranes to produce 10% NaCl solution in the concentratingcompartment. Stage 1 in ED train 2 would operate at about 70% recoveryto produce the brine solution. ED Stage 2 has an estimated recovery of48%. The overall recovery of ED train 2 is about 40%.

The at least partially treated product water has a TDS of about 2,500ppm with high content of calcium, magnesium ions from the two trains.The at least partially treated water stream would be softened thesoftener or ion exchanging unit to exchange calcium and magnesium ionstherein for sodium ions. The softened feed from the softener to thedownstream CEDI train should not have a tendency to form scale duringdesalination to the target drinking water quality. The softener isperiodically regenerated by the 10% brine solution supplied by ED train2, stage 1.

The electrodeionization device provides transport of Na⁺ and Cl⁻ ionsfrom the brine stream (10% NaCl) into a reject stream. Transport ofcounter-ions from the diluting stream into the reject stream shouldmaintain electroneutrality. The net thermodynamic voltage across thestreams is reduced because at least a portion of the DC voltage isgenerated by the half-cell pairs. Although not illustrated, any of theEDI reject streams can be recycled to the feed into the ED devices.

The effluent from the brine compartments can be discharged to a storagetank for use as a softener regenerant.

Some of the simulation parameters (TDS concentration and flow rates)include (with reference to FIGS. 2 and 3):

Inlet Seawater inlet: 35,700 ppm 25,277 m³/hr First Treatment StageFirst ED Train 220, First ED Device 321A and Second ED Device 322B Inletseawater to depletion compartment 321D1: 3,100 m³/hr Inlet seawater toconcentration compartment 321C1: 5,167 m³/hr Reject from compartment321C1: 49,929 ppm Inlet to depletion compartment 322D2: 10,000 ppm 3,100m³/hr Inlet seawater to concentration compartment 322C2: 2,067 m³/hrReject from compartment 322C2: 49,929 ppm Product water 321 fromcompartment 322D2: 2,500 ppm Brine from ED train 222: 99,500 ppm SecondED Train 222 Third ED Device 323A and Fourth ED Device 324B Inletseawater to depletion compartment 323D1: 4,900 m³/hr Inlet seawater toconcentration compartment 323C1: 2,100 m³/hr Outlet Brine fromcompartment 323C1: 99,467 ppm (10% salinity) Inlet to depletioncompartment 324D2: 10,000 ppm Inlet seawater to concentrationcompartment 324C2: 5,277 m³/hr Reject from compartment 324C2: 42,664 ppmOutlet from compartment 324D2: 2,500 ppm Second Stage Inlet to softener330: 2.500 ppm Third Treatment Stage Electrodeionization device 340Inlet to depleting compartment 511: 8,000 m³/hr Inlet seawater to firstconcentrating compartment 541: 2,667 m³/hr Inlet to compartment 512(brine): 2,100 m³/hr (10% salinity) Outlet brine from compartment 512:91,848 ppm Product Outlet from compartment 511: 500 ppm

TABLE 2 ED overall ED/EDI overall TDS in feed to product stream 35,700ppm 35,700 ppm TDS in feed to reject stream 35,700 ppm 35,700 ppmRecovery 39.9% 32.9% Flow rate per membrane area 1.79 gfd 1.60 gfd(flux) 0.0030 m/hr 0.0027 m/hr Product TDS 2,500 ppm 500 ppm RejectTDS - Stage 1 thru 99,467 ppm Stage 5 Reject TDS - Stage 6 thru 42,664ppm Stage 7 Total power 1,706 kW 1,799 kW Total energy required per unit1.39 kWh/m³ 1.47 kWh/m³ product 5.27 kWh/Kgal 5.56 kWh/Kgal Membranearea per flow rate 0.560 ft²/gpd 0.627 ft²/gpd 329.9 m²/(m³/hr) 369.1m²/(m³/hr) Product flow rate 1,225 m³/hr 1,225 m³/hr Reject flow rateStage 1 thru 5 525 m³/hr Reject flow rate Stage 6 and 7 1,319 m³/hrReject flow rate, ED total 1,844 m³/hr Reject flow rate, ED/EDI total2,504 m³/hr Total projected membrane 404,068 m² 452,171 m² area

TABLE 3A Stage 1 2 3 TDS in feed to 35700 ppm 30000 ppm 25000 ppmproduct stream TDS in feed to reject 35700 ppm 52800 ppm 64467 ppmstream Total voltage drop 0.0584 Volt 0.0632 Volt 0.0744 Volt per cellpair Recovery 75.0% 70.0% 70.0% Flow rate per 25.0 gfd 25.0 gfd 25.0 gfdmembrane area (flux) 0.0174 gpm/ft² 0.0174 gpm/ft² 0.0174 gpm/ft² 0.0424m/hr 0.0424 m/hr 0.0424 m/hr Product TDS 30000 ppm 25000 ppm 20000 ppmReject TDS 52800 ppm 64467 ppm 76133 ppm Total power 196.7 kW 186.8 kW220.1 kW Total energy required 0.161 kWh/m³ 0.153 kWh/m³ 0.180 kWh/m³per unit product 0.61 kWh/Kgal 0.58 kWh/Kgal 0.68 kWh/Kgal Membrane areaper 0.04 ft²/gpd 0.04 ft²/gpd 0.04 ft²/gpd flow rate 23.56 m²/(m³/hr)23.56 m²/(m³/hr) 23.56 m²/(m³/hr) Product flow rate 1225 m³/hr 1225m³/hr 1225 m³/hr Reject flow rate 408 m³/hr 525 m³/hr 525 m³/hr Totalprojected 28862 m² 28862 m² 28862 m² cation membrane area Totalprojected anion 28862 m² 28862 m² 28862 m² membrane area Total projected57724 m² 57724 m² 57724 m² membrane area

TABLE 3B Stage 4 5 6 TDS in feed to 20000 ppm 15000 ppm 10000 ppmproduct stream TDS in feed to reject 76133 ppm 87800 ppm 35700 ppmstream Total voltage drop 0.0892 Volt 0.1110 Volt 0.1160 Volt per cellpair Recovery 70.0% 70.0% 65.0% Flow rate per 25.0 gfd 25.0 gfd 25.0 gfdmembrane area (flux) 0.0174 gpm/ft² 0.0174 gpm/ft² 0.0174 gpm/ft² 0.0424m/hr 0.0424 m/hr 0.0424 m/hr Product TDS 15000 ppm 10000 ppm 5000 ppmReject TDS 87800 ppm 99467 ppm 44986 ppm Total power 263.8 kW 328.2 kW342.9 kW Total energy required 0.215 kWh/m³ 0.268 kWh/m³ 0.280 kWh/m³per unit product 0.82 kWh/Kgal 1.01 kWh/Kgal 1.06 kWh/Kgal Membrane areaper 0.04 ft²/gpd 0.04 ft²/gpd 0.04 ft²/gpd flow rate 23.56 m²/(m³/hr)23.56 m²/(m³/hr) 23.56 m²/(m³/hr) Product flow rate 1225 m³/hr 1225m³/hr 1225 m³/hr Reject flow rate 525 m³/hr 525 m³/hr 660 m³/hr Totalprojected 28862 m² 28862 m² 28862 m² cation membrane area Totalprojected anion 28862 m² 28862 m² 28862 m² membrane area Total projected57724 m² 57724 m² 57724 m² membrane area

TABLE 3C Stage 7 EDI TDS in feed to 5000 ppm 2500 ppm product stream TDSin feed to reject 35700 ppm 35700 ppm stream Total voltage drop 0.1133Volt 0.0788 Volt per cell pair Recovery 65.0% 70.0% Flow rate per 25.0gfd 60.0 gfd membrane area (flux) 0.0174 gpm/ft² 0.0417 gpm/ft² 0.0424m/hr 0.1019 m/hr Product TDS 2500 ppm 500 ppm Reject TDS 40343 ppm 40367ppm Total power 167.5 kW 93.2 kW Total energy required 0.137 kWh/m³0.076 kWh/m³ per unit product 0.52 kWh/Kgal 0.29 kWh/Kgal Membrane areaper 0.04 ft²/gpd 0.02 ft²/gpd flow rate 23.56 m²/(m³/hr) 9.82 m²/(m³/hr)Product flow rate 1225 m³/hr 1225 m³/hr Reject flow rate 660 m³/hr 525m³/hr Total projected 28862 m² 24052 m² cation membrane area Totalprojected anion 28862 m² 24052 m² membrane area Total projected 57724 m²48103 m² membrane area

TABLE 4 Combined Combined ED and ED Train 1 ED Train 2 ED Stages EDIStage EDI Product Flowrate, 8,000 m³/hr Power Requirement, 3,938 6,82410,762 628 11,390 kW Energy Requirement 0.492 0.853 1.345 0.079 1.424per cubic meter of product, kW/m³

Example 4

This example describes a Donnan-enhanced EDI device in accordance withone or more aspects of the invention. FIG. 8 shows a schematic of theDonnan-enhanced EDI process, with four cells identified as the“repeating unit” in a module.

In the absence of an applied electric field, anions in the brine streamB1 are transferred towards the concentrating stream C1B on the rightacross the separating anion exchange membrane due to concentrationdifference between the brine and concentrating streams. To maintainelectroneutrality, an equivalent amount of cationic species, on a chargebasis, would typically migrate from the diluting stream D1 into theconcentrating stream C1B, across the cation selective membrane CM.Similarly, cationic species typically migrate from the brine stream B1into the concentrating stream C1A across another cation selectivemembrane CM. To maintain electroneutrality, anionic species typicallymigrate from the diluting stream D2 into the concentrating stream CIA,across the anion selective membrane AM. In effect, transfer of ions froma brine stream into the adjacent concentrating streams due toconcentration difference can be considered as promoting migration ofionic species from the diluting streams to the concentrating streams tomaintain electroneutrality. The diluting streams are thereforedeionized.

If a direct current DC electric field is applied, the ionic transfer dueto the electric field can be augmented by the ionic migration phenomenadue to the concentration difference between the brine and adjacentconcentrating streams in a process referred to as Donnan-enhanced EDI,which is based on the Donnan potential that arises as a result of aconcentration difference of ions across an ion exchange membranepermeable to those ions.

Example 5

This example describes alternative configurations of the treatmentsystem and techniques of the invention, utilizing ED devices, withsoftening and EDI devices to desalinate brackish and seawater.

FIGS. 9 and 9B show further embodiments of the treatment system inaccordance with one or more aspects of the invention. In contrast to thesystem illustrated in FIG. 2, the treatment system 905 further utilizesa third train electrodialysis units ED TRAIN 3 disposed to receive theat least partially treated water and further treat the water stream byremoving at least a portion of target species before ion exchange andfurther treatment in the third treatment stage which can be aDonnan-enhanced electrodeionization device (DE-EDI). FIG. 9B showsanother exemplary treatment system 910 that also utilizes a third trainelectrodialysis units ED TRAIN 3, which is also disposed to receive theat least partially treated water and further treat the water stream, butinstead utilizes a conventional EDI without a brine stream, or an EDIwith polarity and flow reversal (EDIR), rather than an DE-EDI device.

The EDI R device is disposed downstream from the IX softener and maytolerate higher hardness feed streams which can allow lower softenerhardness removal, or higher hardness breakthrough before regeneration.Higher breakthrough conditions would increase the time between IXsoftener unit regenerations and may also reduce the size and capital andoperating cost of the softeners.

Further variation or modifications of the systems of FIGS. 9A and 9B mayinvolve, for example, disposing the IX softener before ED TRAIN 3.

Such systems may be utilized to desalinate seawater as well as brackishwater from estuaries, rivers and/or even groundwater.

Example 6

In this example, desalination experiments were performed usingelectrodialysis modules which had either standard or monovalentselective membranes. The initial feed solution was either an about35,000 ppm NaCl solution or synthetic seawater with about 35,000 ppmtotal dissolved solids (TDS).

FIGS. 11A and 11B show the calculated energy required per m³ of EDproduct as the target concentration in the product stream was reducedfrom about 35,000 ppm to about 500 ppm, using standard ion selectivemembranes (FIG. 11A) and monovalent selective membranes (FIG. 11A). Themonovalent selective membranes used were the CMS cation selectivemembrane and the AMS anion selective membrane from Tokuyama Soda Co.,Tokyo, Japan. FIGS. 12A and 12B shows the fractions cationic species(FIG. 12A) and anionic species (FIG. 12B) remaining relative toelectrodialysis stages utilizing monovalent selective membranes.

For both types of ED modules, the energy consumption is higher when thefeed is synthetic seawater. The ratio of energy consumption for seawatercompared to the synthetic NaCl solution range from 17%-32% for an EDmodule with standard membranes and 21% for an ED module with monovalentselective membranes.

The energy consumption is much higher for an ED module with monovalentmembranes, almost twice that of an ED module with standard membranes.

The energy consumption increased steeply as the target product TDS wasreduced below about 5,000 ppm.

Seawater contains divalent ions such as Ca⁺, Mg⁺, and SO₄ ²⁻ in additionto NaCl, as shown listed above in Example 1, which can affect thedivalent ions energy consumption, as illustrated with the data betweenseawater vs. and synthetic NaCl solution.

Because monovalent selective membranes preferentially allow passage ofmonovalent ions relative to divalent ions, it is believed that the thatthe ratio of concentrations of divalent to monovalent ions in thediluting compartments would increase as seawater is desalinated in aseries of ED modules. FIGS. 12A and 12B show the fraction of ionsremaining in an experiment with ED modules with monovalent selectivemembranes. The data show that the membranes retard passage of divalentions relative to monovalent ions. The selectivity of the anion membraneis almost 100%, which is consistent with published data on the TokuyamaSoda monovalent selective anion membranes. A perfectly selective anionmembrane would result in no transfer of SO₄ ions and therefore theamount of SO₄ ions remaining would remain at 100%. It is believed thatthe increase in SO₄ concentration is due to a electroosmosis phenomena,whereby water is also transported through the membranes.

Based on FIGS. 12A and 12B, it is believed that the higher energyconsumption in ED modules with monovalent selective membranes is due tothe increase in ratio of concentrations of divalent to monovalent ions.It is also expected that removal of divalent ions in the feed water,particularly SO₄, would reduce the energy consumption in both ED and EDImodules. Removal of divalent ions as part of the pretreatment to the EDstep by nanofiltration (NF), for example, would reduce the energyconsumption of both ED and the EDI step. The NF product would thereforecontain primarily NaCl and KCl at a lower concentration than thestarting seawater and would require less energy to desalinate to 500ppm. Thus, in some configurations of the invention, NF operations as apressure driven process can be utilized to facilitate recovery, and theenergy spent and remaining in the NF reject would further reduce thesystem energy consumption. Energy recovery devices, originally developedfor reverse osmosis (RO), are believed to be applicable also to NF unitoperations.

Alternatively, a salt regenerated anion exchange step ahead of the EDdevices or between the ED and the EDI devices would also reduce theoverall energy consumption.

Some aspects of the present invention provide systems and techniques ofseawater desalination through electrically driven processes. Transfer ofions facilitated by an electrical potential is described as a relativelyefficient process because the resistance to ion movement is limited bythe membranes that are used to separate purified water from thewaste/concentrated water. Additional features and aspects of theinvention can pretreatment operation as described herein.

Having now described some illustrative embodiments of the invention, itshould be apparent to those skilled in the art that the foregoing ismerely illustrative and not limiting, having been presented by way ofexample only. Indeed, some exemplary configurations of the device,systems, and techniques of the invention and particular componentsimplemented in such configurations are considered a part of the presentdisclosure. For example, each of the unit operations when describedherein as being connectable or being connected, such as fluidlyconnected, involve respective inlet and outlet ports that provide suchconnectivity. Non-limiting examples of connecting structures includepipes and threaded or welded flanges secured by bolts and nuts, andtypically sealed with gaskets. Numerous modifications and otherembodiments are within the scope of one of ordinary skill in the art andare contemplated as falling within the scope of the invention. Inparticular, although many of the examples presented herein involvespecific combinations of method acts or system elements, it should beunderstood that those acts and those elements may be combined in otherways to accomplish the same objectives.

Those skilled in the art should appreciate that the parameters andconfigurations described herein are exemplary and that actual parametersand/or configurations will depend on the specific application in whichthe systems and techniques of the invention are used. Those skilled inthe art should also recognize or be able to ascertain, using no morethan routine experimentation, equivalents to the specific embodiments ofthe invention. It is therefore to be understood that the embodimentsdescribed herein are presented by way of example only and that, withinthe scope of the appended claims and equivalents thereto, the inventionmay be practiced otherwise than as specifically described.

Moreover, it should also be appreciated that the invention is directedto each feature, system, subsystem, or technique described herein andany combination of two or more features, systems, subsystems, ortechniques described herein and any combination of two or more features,systems, subsystems, and/or methods, if such features, systems,subsystems, and techniques are not mutually inconsistent, is consideredto be within the scope of the invention as embodied in the claims.Further, acts, elements, and features discussed only in connection withone embodiment are not intended to be excluded from a similar role inother embodiments.

As used herein, the term “plurality” refers to two or more items orcomponents. The terms “comprising,” “including,” “carrying,” “having,”“containing,” and “involving,” whether in the written description or theclaims and the like, are open-ended terms, i.e., to mean “including butnot limited to.” Thus, the use of such terms is meant to encompass theitems listed thereafter, and equivalents thereof, as well as additionalitems. Only the transitional phrases “consisting of” and “consistingessentially of,” are closed or semi-closed transitional phrases,respectively, with respect to the claims. Use of ordinal terms such as“first,” “second,” “third,” and the like in the claims to modify a claimelement does not by itself connote any priority, precedence, or order ofone claim element over another or the temporal order in which acts of amethod are performed, but are used merely as labels to distinguish oneclaim element having a certain name from another element having a samename but for use of the ordinal term to distinguish the claim elements.

1.-15. (canceled)
 16. A seawater desalination system, comprising: atleast one first electrodialysis device including at least one firstdepletion compartment having a first depletion compartment inlet fluidlyconnected to a source of seawater, and a first depletion compartmentoutlet, and at least one first concentration compartment having a firstdepletion compartment inlet and a first depletion compartment outlet; atleast one second electrodialysis device including at least one seconddepletion compartment having a second depletion compartment inletfluidly connected to the source of seawater, and a second depletioncompartment outlet, and at least one second concentration compartmenthaving a second concentration compartment inlet fluidly connected to thesource of seawater, and a brine outlet; at least one ion exchanging unithaving an ion exchanger inlet fluidly connected to at least one of thefirst depletion compartment outlet and the second depletion compartmentoutlet, and an ion exchanger outlet; and at least oneelectrodeionization device having a first depleting compartment fluidlyconnected to the ion exchanger outlet, the depleting compartment definedat least partially by a first cationic selective membrane and a firstanionic selective membrane, a first concentrating compartment fluidlyconnected to the source of seawater, and in ionic communication with thefirst depleting compartment through the first cationic selectivemembrane, and a second depleting compartment fluidly connecteddownstream from the brine outlet, and in ionic communication with thefirst concentrating compartment through a second anionic selectivemembrane.
 17. The seawater desalination system of claim 16, wherein atleast one of the first concentrating compartment and the seconddepleting compartment does not contain ion exchange resin.
 18. Theseawater desalination system of claim 16, wherein the at least oneelectrodeionization device further comprises a second concentratingcompartment at least partially defined by the first anionic selectivemembrane, and having an inlet fluidly connected to the source ofseawater, and a third depleting compartment in ionic communication withthe second concentrating compartment through a second cationic selectivemembrane, and having an inlet fluidly connected to at least one of thebrine outlet, an outlet of the first concentrating compartment, and anoutlet of the second depleting compartment.
 19. The seawaterdesalination system of claim 18, wherein at least one of the firstconcentrating compartment, the second depleting compartment, the secondconcentrating compartment, and the third depleting compartment does notcontain ion exchange resin.
 20. The seawater desalination system ofclaim 16, further comprising a brine storage tank fluidly connected toat least one of an outlet of the first concentrating compartment and anoutlet of the second depleting compartment.
 21. The seawaterdesalination system of claim 20, wherein the brine storage tankcomprises an outlet fluidly connectable to the at least one ionexchanging unit.
 22. The seawater desalination system of claim 21,further comprising a third electrodialysis device having a thirddepletion compartment fluidly connected downstream from the firstdepletion compartment and upstream of the ion exchanging unit.
 23. Theseawater desalination system of claim 22, further comprising a fourthelectrodialysis device having a fourth depletion compartment fluidlyconnected downstream from the second depletion compartment and upstreamof the ion exchanging unit.
 24. The seawater desalination system ofclaim 16, wherein the at least one first electrodialysis devicecomprises a monovalent selective membrane disposed between the at leastone first depletion compartment and the at least one first depletioncompartment.
 25. The seawater desalination system of claim 24, whereinthe first depleting compartment of the electrodeionization devicecontains a mixed bed of ion exchange media.
 26. The seawaterdesalination system of claim 16, further comprising at least onepretreatment unit operation fluidly connected downstream from the sourceof seawater and upstream of at least one of the at least one firstelectrodialysis device, the at least one second electrodialysis device,and the at least one electrodeionization device.
 27. The seawaterdesalination system of claim 26, wherein the at least one pretreatmentunit operation comprises at least one subsystem selected from the groupconsisting of a filtration system, a chlorination system, adechlorination system, and a pressure-driven system.
 28. The seawaterdesalination system of claim 27, wherein the pretreatment unit operationcomprises at least one of a microfilter, a sand filter, a particulatefilter, and a nanofiltration system.
 29. The seawater desalinationsystem of claim 16, wherein at least one of the at least oneelectrodeionization device comprises an anodic collector, a cathodiccollector, and a salt bridge in ionic communication with the anodic andthe cathodic collectors.
 30. The seawater desalination system of claim16, wherein at least one of the at least one electrodeionization device,the at least one first electrodialysis device, and the at least onesecond electrodialysis device comprises an anode compartment fluidlyconnected downstream from a source of an aqueous solution havingdissolved chloride species, the anode compartment comprising one of achlorine outlet and hypochlorite outlet.
 31. The seawater desalinationsystem of claim 16, wherein at least one of the at least one theelectrodeionization device, the at least one first electrodialysisdevice, and the at least one second electrodialysis device comprises asecond electrode compartment comprising a caustic stream outlet.
 32. Theseawater desalination system of claim 16, wherein the at least one ionexchanging unit comprises chloride-form anion exchanging resin.
 33. Adesalination system, comprising: means for selectively reducing aconcentration of monoselective species in a first seawater stream toproduce a first diluted stream; means for increasing a dissolved solidsconcentration in a second seawater stream to produce a brine stream;means for exchanging at least a portion of divalent species formonovalent species in the first diluted stream, the means for exchanginghaving a second diluted stream outlet; and an electrochemical separationdevice having a depleting compartment fluidly connected to the seconddiluted stream outlet, and means for providing a concentration-inducedelectrical potential in ionic communication with the depletingcompartment.
 34. The desalination system of claim 33, wherein the meansfor increasing a dissolved solids concentration in the first seawaterstream comprises an electrodialysis device having a depletioncompartment fluidly connected to the source of seawater, and aconcentration compartment separated from the depletion compartment by amonovalent selective membrane.
 35. The desalination system of claim 33,wherein the means for increasing a dissolved solids concentration in thesecond seawater stream comprises an electrodialysis device having aconcentration compartment fluidly connected to the source of seawater,and a brine outlet providing the brine stream.
 36. The desalinationsystem of claim 35, wherein the means for providing aconcentration-induced electrical potential comprises a first half-cellcompartment fluidly connected to a source of a first half-cell feedstream having a first concentration of total dissolved solids, and asecond half-cell compartment fluidly connected to a source of a secondhalf-cell feed stream having a second concentration of total dissolvedsolids that is greater than the first concentration of total dissolvedsolids.
 37. The desalination system of claim 36, wherein the firsthalf-cell compartment is fluidly connected to a source of seawater andthe second half-cell compartment is fluidly connected to a source ofbrine.
 38. An electrodeionization device comprising: a depletingcompartment fluidly connectable to a source of water having dissolvedsolids therein, the depleting compartment defined at least partially bya cationic selective membrane and a first anionic selective membrane;and a concentration cell pair ionically communicable with the depletingcompartment, the concentration cell pair comprising a first half-cellcompartment fluidly connectable to a source of a first aqueous liquidhaving a first dissolved solids concentration, and ionicallycommunicable with the depleting compartment through one of the cationicselective membrane and the first anionic selective membrane, and asecond half-cell compartment fluidly connectable downstream from asource of a second aqueous liquid having a second dissolved solidsconcentration that is greater than the first dissolved solidconcentration, and ionically communicable with the first half-cellcompartment through a second anionic selective membrane.
 39. Theelectrodeionization device of claim 38, wherein the first aqueous liquidis seawater.
 40. The electrodeionization device of claim 39, wherein thesecond aqueous liquid is brine having a second dissolved solidsconcentration of at least about 10 wt %.
 41. The electrodeionizationdevice of claim 38, wherein a ratio of the second dissolved solidsconcentration to the first dissolved solids concentration is at leastabout
 3. 42.-48. (canceled)